It is known for vehicles having active telematics units to communicate vehicle diagnostic data. However, instances can arise where it is desirable to communicate vehicle diagnostic data even though the vehicle's telematics unit is inactive. For example, a vehicle telematics unit may be inactive because an account subscriber has elected to stop paying for a telematics-based service. In such a case, the telematics unit may be lacking a mobile dialing number/mobile identification number (MDN/MIN) so that it cannot engage in conventional two-way telephony.